1. Technical Field
The present invention generally relates to devices and methods employing such devices for concrete paving. More particularly, the present invention relates to devices and methods for crack control in monolithic pour concrete paving.
2. Related Art
Concrete is widely used in a variety of construction, projects, in particular, in pavement structures such as sidewalks, roads, highways, runways, and other flat and open spaces. However, it is well known that such concrete structures frequently exhibit cracking along unpredictable lines due to thermal expansion and contractions, shrinkage resulting from hydration during the curing process, and stresses applied thereto from foot and vehicular traffic. Typical contraction rates for concrete are about one-sixteenth of an inch for every ten feet of length. A number of effective techniques are known for controlling the location and direction of the cracks. These techniques generally involve segregating large concrete pours into smaller segments that allow the concrete to crack in straight lines along the joint between the segments as expansion and contraction occurs.
One method involves placing forms in a checkerboard pattern. A first batch of plastic/wet concrete is poured into alternating areas of the checkerboard pattern. After curing, the forms may be removed and expansion joint material may be positioned adjacent to edges of the cured area. Thereafter, the remaining areas in the checkerboard pattern are poured with a second batch of plastic concrete. This technique is referred to in the art as forming “cold joints” between the first concrete pour and the second concrete pour. Further, as a means of preventing bucking or angular displacement of such cold joints, it is common practice to insert smooth steel dowel rods generally known as “slip dowels” within the edge portions of adjoining concrete blocks in such a manner that the concrete blocks may slide freely along one or more of the slip dowels, permitting linear expansion and contraction of the blocks while also maintaining the blocks in a common plane and thus preventing undesirable bucking or unevenness of the cold joint. As will be appreciated by those having ordinary skill in the art, the aforementioned method is both labor intensive and time consuming because of multiple curing steps and the requirement of removing the forms after each such curing step.
Alternatively, the entire structure may be constructed with a single pour of concrete, the technique otherwise referred to as a monolithic pour. While some monolithic pour techniques utilize forms and dowels embedded within the structure much like the multiple-pour techniques, other techniques involve no intermediate forms segregating one segment from the other. Control joints were utilized instead, which were deliberately weakened sections of the poured concrete. During expansion and/or contraction, these weakened sections were the first to crack, thereby forming sections of the concrete structure that transform independently of another.
One common way of forming such a control joint is by saw-cutting an elongate groove through the upper surface portion of the structure after partial curing of the concrete. This technique was unsatisfactory in a number of respects. Sawing grooves within concrete is expensive and tedious work, and requires an intermediate visit to the site after the concrete has been poured and allowed to partially cure. If an attempt is made to cut the grooves within the concrete at too early of a time, the grooves will have undesirably irregular configurations. On the other hand, if too much time is allowed to elapse before cutting the grooves, random cracking and separation of the concrete will occur at other locations in the structure. Additionally, the finished control joints are wide and unsightly, and the edges of the concrete defining the control joints are subject to considerable degradation over time. Manual sawing often results in crooked grooves, and although machinery has been developed to correct this deficiency, such machinery is cumbersome to operate and expensive to acquire.
On a related note, most conventional concrete pavement utilize Portland cement concrete, which will be appreciated as being a dull, gray color upon curing. Accordingly, there is a demand for variations in color and surface texture of concrete such that the concrete posses improved aesthetics similar to traditional flooring surfaces such as marble, stone and granite. Surface seeded exposed aggregate concrete such as that disclosed in U.S. Pat. No. 4,748,788 to Shaw, et al., has met this demand.
In addition to the deficiencies described above, it is understood that sawing grooves in surface seeded aggregate concrete is particularly deficient. Since the aggregate is suspended in the concrete, sawing into the same resulted in the aggregate becoming dislodged from the remainder of the concrete. This results in less desirable surface aesthetics, and weakens structural integrity by leaving pockets in the concrete.
Alternative techniques have been considered that avoid the problems of sawing grooves to form control joints, such as the “Zip Strip” expansion joint manufactured by Sandell Manufacturing Company, Inc. of Schenactady, N.Y. The Zip Strip includes an elongate rail with a removable cap. The rail is inserted into wet concrete, and the cap suspends the assembly in the concrete. Upon partially curing the concrete, only the cap is removed, and the rail provides a weakness in the concrete from which a crack or fracture can occur. Although capable of being used with surface-seeded aggregate concrete as discussed above, one deficiency with the Zip Strip was that the rail remained visible upon completion since it was necessary for the same to remain within the concrete after curing. Additionally, it is difficult to properly align the rail and the cap in plastic concrete, particularly where multiple control joints are involved.
Accordingly, there is a need in the art for an improved crack control device for use in conjunction with monolithic pour concrete structures and techniques for constructing the same, such devices and methods overcoming the deficiencies in the art as set forth above.